Seasonal influenza infection is a major health concern for first-world and developing nations alike. Each year in the United States, five- to twenty-percent of the population gets the flu, more than 200,000 people are hospitalized from flu complications, and about 36,000 people die from flu. Worldwide, influenza causes tens of millions of respiratory illnesses and 250,000 to 500,000 deaths each year. New strains of avian influenza that are transmissible to humans are a critical concern for global health because these flu strains could yield pandemic disease for which no immunity exists, potentially resulting in millions of fatalities. “Avian flu” refers to a pathogenic avian influenza subtype that is highly contagious among birds and causes high mortality among domestic poultry. Outbreaks of avian flu among poultry and wild birds are ongoing in a number of countries, and at least three subgroups of avian flu viruses have infected humans to date. While avian flu infections of humans are rare, and most cases have been associated with direct poultry contact during outbreaks among livestock, infection in humans is very serious when it does occur: to date, over half of all reported human cases have been fatal. Since first reported in Hong Kong in 1996, the World Health Organization has carefully tracked avian flu and instances of animal-to-human influenza transmission, with confirmed cases reported from China, Indonesia, and Southeast Asia; Pakistan; Iraq; Egypt; and elsewhere, with 385 cases resulting in 243 deaths worldwide. While there is no evidence of sustained human-to-human transmission, instances of human-to-human spread of avian flu may have occurred. Since all influenza viruses have the ability to rapidly mutate, there is considerable concern that avian flu may be able to infect humans more easily and become communicable from one person to another. Also, avian flu virus strains have not infected many humans worldwide, so there is little or no immune protection against these strains in the human population; therefore, an influenza pandemic could easily occur if sustained avian flu virus transmission were to develop.